The ESD file is essentially an encrypted and compressed version of their previous WIM fileformat (it can actually be decrypted back to a WIM image file). ESD is a Windows imagingfile that contains a full copy of the Windows operating system in a protected container.The comparison between a WIM disk image and a ESD install compressed disk image file isthat the ESD file is typically approximately 30 percent smaller inside which can make itfaster to download and install for updating purposes.